100-400 with Canon Teleconverter 1.4 Mark III - Not impressed

I recently bought a TC 1.4 Mark III. Just want to share some of my test results with 100-400 lens. I do not think this combination works at all. I understand the TC is not designed for zoom lens like this.

I cropped the photo in order to show 100% size. This is the one took without TC:

This one took with TC on:

I have done many tests, some with different subject and some with tripod on. I found the result is consistent. The photo without TC is sharp of course, however, even when I enlarge the photo to 1.4 times in Photoshop, it is still sharper than the one took with TC.

This made me believe that 100-400 with TC is completely useless. Or maybe my TC is a bad copy? Any comments?